1. Field of the Invention
The present invention pertains to climate chambers, including an endless conveyor belt which is coiled to have multiple tiers in a generally helical stack.
2. Description of the Prior Art
Many mass production manufacturing operations today include conveyors for transporting articles through a climate chamber. Climate chambers in general can operate over a wide range of temperatures and ambient conditions, with examples including large ovens for cooking, sterilizing curing or heating, as well as refrigeration chambers for cooling or freezing, and chambers for humidifying, dehumidifying, drying, and otherwise treating products with a gas or vapor. Climate chambers offer an economy of production in that they allow a continuous mass processing of articles, as opposed to batch processing, within a relatively confined space. A need has arisen, however, to develop improved reliable conveyor systems for transporting a continuous succession of articles through the climate chambers. In the food processing industry, fresh vegetables, cooked vegetables, raw ground meat, cooked fish, loose French fries, and other food products are received or are preliminarily prepared at a wide variety of temperatures before being introduced for mass processing in large climate chambers. Some products have loose components, such as unfrozen pizza toppings, which are susceptible to being blown off by air currents within a climate chamber, or they may become airborne and lifted when carried on perforated conveyor belts. Other food products, such as unfrozen soft meat patties, may be disturbed if placed on a conveyor belt prior to the belt being collapsed on one side for coiling in a helical stack. Access from the exterior of the belt stack is needed to load meat patties on an already coiled portion of the conveyor belt. A commercially successful conveyor belt design must meet these and other needs that arise in the food processing industry as well as other industries.
Two different types of conveyor systems are used today in the food processing industry. Both conveyor systems have endless belts which are flexible in horizontal as well as vertical directions, allowing them to follow paths which include helical turns or tiers through the climate chamber as well as looping turns of various sizes which align the belts with loading and unloading equipment at the entrance and exit portions of the climate chamber, and with equipment for driving and, on occasion, cleaning the belt. One notable difference between the two types of systems is observed in the support of the helical turns or tiers of the conveyor belt.
An example of one conveyor system is given in U.S. Pat. No. 3,348,659, in which various spiral or helical tiers of a collapsible conveyor belt are separated from one another, sliding on two parallel paths of helical rails located adjacent each lateral edge of the belt. The rails, in turn, are carried by rigid supports extending laterally across the width of the conveyor belt, located underneath to support the weight thereof. The rigid supports in combination with the rails, form a ladder-like helical path underlying the helical turns or tiers of the conveyor belt. This conveyor system can be driven from a central rotating drum having a vertical axis which contacts the inboard edges of the belt, providing the frictional or mechanical engagement necessary to advance the belt along its defined path. The rail-mounted conveyor belt with stationary supporting structures extending between belt tiers has reduced head space clearance for products carried on the product-bearing horizontal surface or weblike bed of the conveyor belt. Considerable space between tiers is taken up by the rails and framework supporting the rails. It has also been observed that products unevenly loaded on the belt, for example, one product partially overlying an adjacent product, may contact the stationary support structure as they are moved by the belt. As a result, products may become jammed within the conveyor belt system, requiring a system shutdown so that the jammed products may be removed from the conveyor belt and the belt and the support structure sufficiently cleaned so as to at least allow parts of the belt to move properly and permit adequate conveyor operation. Frequently, the jamming of products on a conveyor belt requires a thorough manual cleaning of the climate chamber, as well as major portions of the conveyor belt, particularly if the products, such as unfrozen meat patties, are soft enough as to become embedded in the crevices of the conveyor belt or in the perforated bed on which the products are placed. In any event, contact between food products and the stationary supports requires increased servicing of the conveyor belt, to maintain hygienic conditions beyond regularly scheduled maintenance which would otherwise be required.
The first type of conveyor system is inefficient in utilization of vertical height, with only about fifty percent utilization in order to provide space so that the product to be treated will not strike the lateral support arms. Also, this inefficiency in vertical height means a considerably larger volume of the climate chamber which must be cooled to operating temperature, in freezer applications, for a given amount of product to be treated. Further, the dirtying of the support arms by piled-up product, and especially the jamming of the entire conveyor belt by piled-up product, not only stops the freezer for clearing the jam and manual cleaning but also stops the entire processing line of cooking, packaging, etc. within the entire food processing plant. This down time is quite expensive in loss of product output.
An example of the second type of conveyor system is given in U.S. Pat. No. 3,938,651, which has a collapsible conveyor belt that is to some extent self-supporting, having upstanding inboard and outboard sidewalls at the lateral edges of a weblike product-supporting bed portion of the belt. The belt is, accordingly, generally U-shaped in cross section. When configured along a helical path, the belt is Wound into helical turns or tiers, stacked one directly on top of the other. The sidewall plates of the belt are, at the various tiers, vertically aligned on their upper and lower edges such that one sidewall plate is stacked above the other, with plates at both the inboard and outboard edges of the helically wound belt forming a pair of nested cylinders. This second type of conveyor system is normally driven from its lower most tier, which supports the weight of the stack.
This type of conveyor system has three main disadvantages:
(1) the complexity of the stack; PA1 (2) the vertical side links on each side of the stack; PA1 (3) the substantially vertical air flow.
As to the first disadvantage, the stack is supported only from the bottom, and hence it is unstable, since it is not well supported laterally. This can cause the entire stack to collapse, which has been known to happen, with severe belt damage as a result. Also, the stack is harder to drive in its helical movement and in practical applications requires two drive chains, one on the inside and one on the outside of the stack, or else requires a wagon train drive belt underneath and supporting the entire stack. Either of these two drive systems is complex, e.g., U.S. Pat. No. 4,565,282, and the several parts to the entire stack and drive system make a less reliable conveyor because of the many moving parts.
The second main disadvantage is the presence of the two side links, one on each side of the belt, which substantially fully enclose the product. The infeed conveyor in the processing plant must be in line with the conveyor system at the infeed in the climate chamber rather than being at an angle thereto which limits the flexibility of positioning. Also, such incoming conveyor must be narrow enough to fit between the side plates of the conveyor system in the climate chamber to again limit the applications in many processing plants. A similar problem is encountered in the outfeed conveyor from the climate chamber: it again must be in line and must be narrow enough to fit between the side plates of the conveyor in the climate chamber. Still further, the side plates on both inside and outside of the conveyor stack means that it is most difficult to inspect the product during processing in the climate chamber and to determine if any problems are arising. Still further, it is hard to treat the product cryogenically with liquid nitrogen or liquid CO.sub.2 because it cannot be sprayed directly on the product for quick freezing because of the presence of the side plates. The presence of the side plates means that the entire belt system is harder to clean, with more moving parts which need to be cleaned. The belt must collapse to permit bending edgewise into a helical path, and if it collapses on the inside of the belt, the side links of the belt can freeze together during travel through a freezer-type climate chamber and then it cannot straighten out properly for the exit from the stack to the exit opening. The presence of the two side links means that the freezer has more mass in the belt with more energy less because the belt travels in and out of the climate chamber at the infeed and the exit, as shown in U.S. Pat. No. 3,938,651, or has a long travel outside the climate chamber, as shown in U.S. Pat. No. 3,412,476, for unloading a product, washing the belt, drying the belt, take-up and infeed of more product. This means the belt is warmed up to room temperature and must again be cooled after entering the freezer chamber, with the extra mass in the belt causing a considerable energy loss. The presence of the two side links means that the structure is poor for a ground meat patty feeder. Such feed cannot be directed radially into the side of the stack because of the side plate and, instead, must be aligned with and on top of the infeed section of the conveyor and be long and thin in order to reach in to place the patties on the already helically formed belt. This long, thin patty loader thus becomes unreliable due to the thin and weak construction.
The third main disadvantage of the second type of conveyor system is the substantially vertical air flow. While all three of the aforementioned prior art patents do show some lateral as well as axial air flow through the stack air flow, the commercially practical conveyor systems have been found to be constrained to substantially vertical air flow. This is because, whereas holes may be shown in the side plates in U.S. Pat. No. 3,938,651, these holes as a practical matter are considerably restricted in size because the side links must be quite sturdy. Each side link must take its turn at the bottom of the stack and must carry the weight of the entire stack and products thereon. As a result, the links must be quite strong and this limits the size of the openings for substantially vertical air flow. This vertical air flow creates a pressure differential between the top and bottom of the stack. This may be only two and a half inches of water differential pressure, which sounds small, but if this is a negative pressure at the bottom of the stack where the infeed occurs, then this creates a high velocity air being drawn into the climate chamber at the opening for the infeed of the conveyor. This high velocity air has been found to be so troublesome that a long baffled tunnel has been used at the entrance in order to attempt to limit the air flow. The high velocity air can cause loose or light products, such as pizza topping, to be blown off the product, or pancakes to be bent double. This results in degraded product quality and product pileup and jamming of the entrance tunnel, so that the entire line must be stopped for cleaning out the entrance tunnel. Other products, such as soft ground raw meat patties, can become damaged, especially in shape, by such high velocity air and pile up in the entrance tunnel. Thus, this requires frequent cleaning of the system and frequent stopping to clear any jams. Further, this pressure differential increases the energy consumption. Energy is also lost by air being bypassed through the tunnel.
The axial air flow encounters resistance of the perforated product-carrying bed portion of the conveyor belt, as well as any products carried on the belt. Thus, in order to ensure a more optimal air flow, it has been found necessary to increase the spacing between products carried on the conveyor belt bed, with the greatest spacing required for larger, sheetlike items of imperforate constitution, such as pies, pizzas, and the like. Even with an increased spacing between products, a significantly high pressure drop between entrance and exit portions of the helical stack results which can also be a problem with multiple layers of items such as potatoes sliced for making French fries. This, in turn, establishes a significantly high pressure drop in the system which circulates the atmosphere of the chamber over the product carried on the conveyor belt.
Alternatives to the tunnel-like baffling include internal walls ("mezzanines") intermediate and parallel to the floor and ceiling of the climate chamber. Such baffling contributes significantly to the frequency with which the climate chamber must be cleaned, and reduces access to internal portions of the climate chamber which is necessary to carry out the cleaning operation. The cost, complexity, and general maintenance of a climate chamber, and at times the size of the climate chamber, are also increased by such baffling.